Abstract:

Article Preview

The present work considers the possibility of simultaneous health monitoring and active repair of the edge debonding in dynamically loaded smart concrete structures strengthened with fiber reinforced plastic (FRP) composite materials. This is achieved by using local piezoelectric (PZT) actuators/sensors, the electro-mechanical admittance concept and extreme value statistics.

Abstract: In the present paper, the repair of a cracked structure under dynamic load using the
electromechanical admittance (EMA) approach is investigated. Conceptually, appropriate electrical
field are applied on the outer surfaces of piezoelectric (PZT) patches to effect closure of the crack.
This has the effect of altering the electromechnaical (E/M) admittance signature, extracted at the
electrical terminals of a specific PZT patch, considered as an admittance calculating sensor (ACS)
patch, towards that of the healthy structure, which is the criterion concept used for the repair in this
paper. To demonstrate the present repair methodology, a cantilever 3D beam numerical example is
considered in combination with a FEM-based minimization of the difference between the healthy
and cracked structure’s (E/M) admittance signature, for specific frequency ranges.

Abstract: This paper presents the use of statistically rigorous algorithms combined with
electromechanical (E/M) impedance approach for health monitoring of engineering structures. In
particular, a statistical pattern recognition procedure is developed, based on frequency domain data
of electromechanical impedance, to establish a decision boundary for damage identification. In
order to diagnose damage with statistical confidence, health monitoring is cast in the context of
outlier detection framework. Inappropriate modeling of tail distribution of outliers imposes
potentially misleading behavior associated with damage. The present paper attempts to address the
problem of establishing decision boundaries based on extreme value statistics so that the extreme
values of outliers associated with tail distribution can be properly modeled. The validity of the
proposed method is demonstrated using finite element method (FEM) simulated data while a
comparison is performed for the extreme value analysis results contrasted with the standard
approach where it is assumed that the damage-sensitive features are normally distributed.

Abstract: Despite that piezoelectric ceramic lead zirconate titanate (PZT) has been used for structural health monitoring (SHM) in various engineering systems, limited work has been conducted on real size concrete structures. Beam-column connections are critical regions in reinforced concrete (RC) moment-resisting frame structures. The vulnerability of RC beam-column joints has been identified from structural damage investigations over the past decades, especially in the area of earthquake engineering. In the context of a terrorist bomb attack, the beam-column joints are very vulnerable, especially when the perimeter columns lose their load carrying capacity due to damage and the beam-column joints become one of the crucial load transfer mechanism of the structural frame. To avoid catastrophic failures, it is important to monitor beam-column joints under existing gravitational loads. In this paper, an experiment is carried out on four real size concrete frame structures with different detailing subjected to gradually increased loads. A number of PZT sensors are bonded to the frame structure to acquire PZT electro-mechanical (EM) admittance signature. The structural mechanical impedance (SMI) is extracted from the PZT EM admittance signature and its sensitivity is compared with that of the EM admittance. The relations between the damage index and the loading step and tip deflection of the concrete structure are obtained. Finally the sensitivity of the PZT sensors in detection of the critical loading level is discussed. The results show that the PZT sensors are capable of monitoring the integrity and behavior of the real size concrete structures.

Abstract: At present, there is no effective online debonding monitoring method for solid rocket motor. In order to solve the problem, the electro-mechanical impedance (EMI) method is introduced into online debonding monitoring for solid rocket motor (SRM). The EMI model of PZT and SRM is developed. The finite element method is employed to analyze the electro-mechanical impedance of the PZT, the conductance curves of PZT are obtained with different damaging phase of SRM, the root-mean-square deviation (RMSD) is used to assess the aging level. The result indicates that EMI as a new detection method is effective in identifying the existence and severity of cracks in SRM. As the debonding area increases, the difference of conductance curves becomes more obvious and the RMSD becomes larger.

Abstract: Nondestructive detection evaluation technique which based on the electro-mechanical impedance (EMI) method is widely used for structure health monitoring (SHM). The arrangement of piezoelectric transducer (PZT) includes two types, surface-mounted and embedded. A lot of researches have been done about two kind of transducer based on EMI method, however the effect of two types on the same damage condition requires to be researched deeply. Therefore, the objective of this investigation is comparing the effect of two kind types of PZT in detecting local damage of concrete beam end. An experiment was set up to detect local damage of the beam by EMI method with both embedded and surface-mounted PZT. The experiment result shows that EMI method is available to detect local damage of concrete beam end. The surface-mounted PZT is more sensitive to local damage of concrete beam end, meanwhile surface-mounted PZT is more vulnerable to the environment and other factors.